Revision as of 16:15, 17 January 2012

Contents

Feature Name

Allow SELinux to turn off all processes ability to ptrace another process.

Summary

This change allows an administrator to prevent all processes on the system from ptrace'ing other processes on the system, including user processes. The ptrace and sys_ptracess access allows one process to read the memory of another process. It also potentially allows one process to manipulate another process, using tools like gdb.

Owner

Current status

Targeted release: [Fedora 17]

Last updated: Tue Jan 17 2012

Percentage of completion: 90%

Detailed Description

The boolean will even prevent the unconfined_t domain from being able to ptrace other domains. Because of this it will be optional and turned off by default. The goal of this change is not to prevent processes with the ability to change booleans from turning the boolean off. This means an unconfined_t process running as root could turn off the deny_ptrace boolean and start ptracing other processes. But an unconfined_t user logged into a system without root privs would not be able to ptrace another process.

Lastly this boolean will only effect policy that is shipped by Fedora, so an admin or third party can ship a package that allows ptrace. You can search for all domains that are allowed to ptrace via the following command.

sesearch -A -p ptrace,sys_ptrace -C | grep -v deny_ptrace

One problem with removing the ptrace permission is currently the "ps -e" command running as root requires ptrace, we need an update to the kernel to change this.

Note: Requires Kernel 3.3 or later to avoid lots of AVC messages.

Benefit to Fedora

The major benefit to Fedora is increased security to know that one process can not read the memory of another process. Meaning if you are running a server with lots of processes running as httpd_t or httpd_sys_content_t, they will be prevented from manipulating other process running with the same label. Similarly processes running by a user will not be able to look at the process memory of other processes. A real world security issue is that processes like gnome-keyring or ssh or firefox which decrypt an encrypted file would have the password sitting in memory. Without this feature a corrupted process would be allowed to examine the other processes memory and potentially steal the secret.

Scope

This change only effects Policy writers and the kernel. Any application like gdb that a programmer or system administrator wanted to run would require the administrator to turn this boolean off.

How To Test

The command

sesearch -A -p ptrace,sys_ptrace -C | grep -v deny_ptrace

On a freshly installed Fedora 17 box should show no output. Turning on the boolean you should see commands like strace and gdb start to fail.

User Experience

Most users should never be bothered by this feature being turned on. A programmer wishing to debug an application would be prevented from running the debugger until he turns the feature off.

We should not be seeing AVC's from common running applications when this boolean is turned on, if we do then a bugzilla should be opened against SELinux.

Certain applications like abrt may use the ability to ptrace/strace a process or applications like NetworkManager that execute gdb to get a traceback on a crash will be blocked by this feature. Although they should not fail to gather as much info as possible.

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